1. Field of the Invention
The invention disclosed herein relates to land vehicles and, in particular, to limiting axial thrust in wheel motors deployed in heavy equipment.
2. Description of the Related Art
Large trucks, such as those used for mining operations, are usually propelled using electric motorized wheel motors. The wheel motors are incorporated into a rear axle of the truck, with a wheel motor driving each dual wheel assembly. In typical wheel motor units, an electric motor is connected to a reduction gearcase, which, in turn, is fastened to a wheel assembly which includes tire and rim assemblies. Tractive power is initiated in the wheel motor while the gearcase functions as torque increaser/speed reducer. As one might imagine, the wheel motors used in large trucks (such as in mining operations) are subject to enormous amounts of wear and stress. Aside from rotational wear and stress, unintended axial thrust can present significant problems.
As an example, in some instances, the gearcase includes a two-stage planetary type gear assembly, with input provided by a floating pinion shaft/gear which is powered by the electric motor. Generally, each planetary stage includes a pinion gear, three planet gears and an outer ring gear.
Under severe torque loading, the planetary gear train can exhibit axial deflections in the meshing gears. These deflections tend to generate axial loading for individual gears and for the planetary stages as a whole. Forces, such as those that may be encountered during normal operation (as well as lateral shock loading), can cause the gearing to run out-of-position and suffer abnormal wear. This can lead to premature gearcase failure and unplanned maintenance events. Clearly, such events come at great expense both in terms of time and money for operators of the heavy equipment.
For the above-mentioned reasons, the gear train must have provisions designed into it to control axial forces and the harmful effects of premature wear. Typically, ball or roller bearings are fitted into the gearcase to control the axial forces in either direction.
In prior art, the bearings are distributed throughout the gearcase and are positioned to control thrust without interfering with the radial meshing of the gearing Interference with the radial float could adversely load the bearing radially and lead to premature failure. Unfortunately, distribution of bearing assemblies throughout the gearcase results in additional manufacturing complexity and tolerance accumulations. Parts count would be higher and the gearcase would require a load bearing bulkhead.
Further, distribution of bearing assemblies in the gearcase also makes the manufacture of each wheel motor more involved, as the bearings must be fitted properly and in specific sequence. During normal maintenance, the bearings cannot be effectively monitored by simple inspection routines, as the bearings are obscured from view. Accordingly, evaluation of bearing wear requires significant disassembly and downtime.
Therefore, what is needed is improved method and apparatus for limiting axial thrust or deflection in the gearcase of a wheel motor. Preferably, the method and apparatus provide users and operators with simplified maintenance and support quick visual inspection with comparatively minimal effort.